Undead Stormwarden Shambler

Dark Discharge. When the Undead Stormwarden Shambler is hit by a melee attack, the attacker must roll a DC 11 Constitution saving throw or be stunned until the end of their next turn. 

Undead Fortitude. If damage reduces the Stormwarden Spellcaster to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Slam. Melee Attack: +3 to hit, reach 5 ft., one creature. Hit: 4 (1d6 + 2) bludgeoning damage. 

Stormscream (1/day). The Undead Stormwarden Shambler unleashes a deafening scream filled with the rage of the storm in a 15-foot cone. Each creature in that area must make a DC 11 Constitution saving throw. On a failed save, a creature takes 9 (2d8)  thunder damage and is pushed 10ft away. On a succesful save, the creature takes half damage and isn't pushed.